The present invention relates to a process for the manufacture of polyphenols, and more specifically to the addition of a catalyst promoter to a reaction mixture for the manufacture of polyphenols.
The compound 2,2-bis(4-hydroxyphenyl)propane, also called para, para-diphenylolpropane or bisphenol-A, is generally prepared by reacting phenol and acetone in the presence of an acidic condensation catalyst along with a catalyst promoter or cocatalyst to increase the reaction rate and selectivity of the condensation catalyst. U.S. Pat. No. 2,468,982 disclosed the use of mercapto substituted aliphatic carboxylic acids as catalyst promoters to increase the condensation reaction rate between phenols and ketones to such an extent that the reaction time could be cut to {fraction (1/10)}th the time previously required. Subsequently, it was discovered that the contact time the acid-catalyzed reaction between phenol and ketones is improved by the use of methyl mercaptans as disclosed in U.S. Pat. No. 2,730,552. Not only was the contact time reduced, but the use of gaseous methyl mercaptan in the reaction zone allowed one to run the reaction with only minimal amounts of catalyst promoter without the formation of any substantial amounts of by-product formation or bisphenol-A product disintegration. Further, methyl mercaptan could be used as a catalyst promoter in a continuous process. It is also distinguished in that its high volatility allows it to be easily separated from the reactor reaction mixture effluent containing bisphenol-A product and avoids the presence of sulfur contaminants in the final product. Since then, the use of gaseous free methyl mercaptan has been the catalyst promoter of choice in acid-catalyzed phenol-acetone reactions.
However, methyl mercaptan is difficult to handle because it is gaseous at room temperature and 1 atmosphere. This makes the shipping of methyl mercaptan inefficient because it must first be pressurized to a liquid state to economically transport sufficient amounts required for the manufacture of bisphenol-A at a plant located some distance from the site producing methyl mercaptan. Moreover, since methyl mercaptan is also hazardous, in some cases shipping this material to certain locations is restricted, resulting in limited availability in these areas. As a result, some bisphenol-A plants must now either produce methyl mercaptan on site, or switch to an alternative catalyst promoter which does not have the volatility of methyl mercaptan.
It is our objective to search for a substance which promotes the acid-catalyzed condensation reaction between phenols and carbonyl compounds at substantially the same rate and with substantially the same selectivity towards bisphenol-A as methyl mercaptan, further without the formation of any by-product sulfur species at levels greater than with the use of methyl mercaptan, but which is not as volatile as methyl mercaptan, which is liquid at room temperature and 1 atmosphere thereby rendering it easily and economically transportable, and which is stable during transport. In essence, we searched for a drop-in replacement for methyl mercaptan which did not possess the shipping and handling disadvantages of gaseous methyl mercaptan.
We originally investigated the use of ethyl mercaptan because it was liquid and is a known catalyst promoter in an acid-catalyzed phenol/ketone reaction. However, the activity of ethyl mercaptan is substantially lower than methyl mercaptan, resulting in longer reaction times. To reduce the reaction time to that of a methyl mercaptan catalyst promoter reaction, three to four times the amount of ethyl mercaptan is needed, resulting in having to use a larger recycle stream containing catalyst promoter back to the reaction zone.
Methyl mercaptan can be converted to its sodium salt in an aqueous solution thereby reducing its volatility and making it much easier to handle and transport. The aqueous salt of methyl mercaptan can also be sent to locations where shipping of pressurized methyl mercaptan in liquid form was restricted. We have also developed a process for regenerating methyl mercaptan from the aqueous salt of methyl mercaptan at the plant location. However, the regeneration of methyl mercaptan adds costs onto the process for making bisphenol-A, and introduces a new effluent stream of sodium acid salt (e.g sodium sulfate or sodium chloride) which must be handled. Accordingly, while the use of aqueous salt of methyl mercaptan solves many of the problems around handling and shipping, it has also introduced a new set of issues which raise the cost of making bisphenol-A by adding gaseous methyl mercaptan to the reaction zone or to one or more reactants.
We have now discovered a catalyst promoter which can be easily shipped and handled due to its relatively low volatility and stability in liquid state during transport. This catalyst promoter has high activity and high selectivity. The amount of sulfur byproduct species produced using this catalyst promoter is low.
There is now provided a condensation process comprising introducing into a reaction zone ingredients comprising a phenolic compound reactant, a carbonyl compound reactant, and a dithioketal catalyst promoter composition, and condensing the phenolic compound and the carbonyl compound in the presence of an acid catalyst.
There is also provided a process for the manufacture of a polyphenol compound comprising introducing into a reaction zone ingredients comprising a phenolic compound reactant, a carbonyl compound reactant, and a catalyst promoter comprising a dithioketal, and reacting the ingredients within the reaction zone in the presence of an acid catalyst.
There is also provided a synthetic method comprising adding together a phenolic compound, a carbonyl compound, and a dithioketal catalyst promoter, hydrolyzing the dithioketal catalyst promoter to its dissociation products, and condensing the phenolic compound and the carbonyl compound in the presence of an acid catalyst and said dissociation products.